Ken And Emma: A Husband-and-wife Dynamic Duo

He's slight and wan and has a shapeless, doughy face like a pre-adolescent boy.

She has a horsy mouth, a perpetually wrinkled brow and it's hard to decide what's sharper - her nose or her jawline.

Fact is, if you were to pass them standing in line at a theater box office, they probably wouldn't warrant a second look. Just an average couple going to the movies.

But put Kenneth Branagh and Emma Thompson in a movie and give them characters to work with and a story to tell - and watch the sparks fly.

Catch their current act in the Branagh-directed Much Ado About Nothing, in which the married couple play Shakespeare's sharp-witted battling lovers, Beatrice and Benedick, and you'll see the most intoxicating kind of movie magic.

Ken and Em are, in fact, poised to become something truly rare in the world of popular movies: a royal couple.

Here's a husband-and-wife team who not only initiate, star in and direct their own films but who also are much in demand to appear in other moviemakers' productions.

Just try to name another married couple who have this sort of enviable profile. Alfred Lunt and Lynn Fontanne ruled the American stage for nearly four decades but never translated their Broadway successes into significant film careers.

Paul Newman and Joanne Woodward's long personal and professional collaboration has brought them close to the status of Hollywood ''royalty'' although their careers essentially are those of actors-for-hire.

Woody Allen and his then-paramour Mia Farrow spent the '80s turning out comedies (and a couple of middling dramas) that tickled the fancies of intellectuals but failed to put a dent in the box office. Besides, we all know how badly that has ended.

On the foreign scene, we've seen such collaborations as Ingmar Bergman and Liv Ullmann (that romance ended 15 years ago), Federico Fellini and Giulietta Masina, or Mike Leigh and Alison Steadman. But most American moviegoers don't even know who these people are.

But Branagh and Thompson could end up with a higher profile than any of the above. Since they were first seen together on the silver screen in 1989 in Branagh's directing debut, Henry V, these two stage actors from the British Isles (he's Irish, she's English) have established themselves as the thinking moviegoer's great hopes.

Branagh has won two Oscar nominations (best actor and best director for Henry V), and Thompson was named best actress (for Howards End). Not bad for a couple age 32 (Branagh) and 33 (Thompson).

They've collaborated on three more films (Much Ado, the Hitchcockian thriller Dead Again and the British Big Chill clone Peter's Friends) and made frequent solo appearances in other films. On top of that, Branagh directs and manages his own London theater company.

So Branagh and Thompson have pretty much cornered the market. Although neither fits the admittedly shallow definition of a ''beautiful person,'' they exude an unpretentious, just-folks aura that makes them endearing. You cannot imagine carrying on a conversation with the likes of, say, Laurence Olivier, but Branagh and Thompson seem very approachable.

Take, for example, Thompson's delightfully down-to-earth mugging at this year's Oscar contest. Her slightly out-of-it bemusement at the whole affair was right on the money, and it was easy to identify with this visitor to Tinseltown.

Furthermore, Thompson seems to know that she's not conventionally gorgeous and is perfectly happy with that fact. The trick is that she's such an intelligent, superbly gifted actress that if she is called upon to play a beautiful woman - voila! - she's suddenly beautiful.

As for Branagh, he runs the risk of being declared a smart-alecky kid. After all, this is a guy who has been compared to Orson Welles as a ''boy wonder'' of the movies and who published his autobiography before he was 30. (He says now he did it only to finance his Renaissance Theatre Company.)

Here again, Branagh dispenses with all traces of pretentiousness. In conversation, he's ribald and admits that, except when it comes to Shakespeare, he's hardly what you would call an intellectual. In many regards, he's still just a Belfast bloke with little taste for high culture.

But with his wife, he shares the ability to transform himself as the role demands. Jerry Harrington, owner of the Tivoli theaters in Kansas City, Mo., said that when Branagh's Henry V opened at his theater, he began noticing repeat business from girls who had been sent to see the film by their English teachers.

When Harrington asked why they were willing to see the film repeatedly, the young women said of Branagh, ''He's hot!''